OLED is driven by a current generated by a driving transistor in a saturation state to emit light. Currently, OLED faces lots of problems mainly including the following.
First, the Low Temperature Poly Silicon (LTPS) process as the main stream manufacturing technology of the OLED driving circuit has very poor uniformity of transistor threshold voltages Vth in the manufacturing procedure, so that different transistor threshold voltages Vth would generate different driving currents with the same input gray-scale voltage, resulting in non-uniformity of the driving currents. In addition to compensating for the differences between the transistor threshold voltages Vth in the LTPS process in the driving circuit, improving the process is also a solution. For example, the oxide thin-film transistor as a very promising panel driving device can obtain very good uniformity in the manufacturing procedure, and can solve the problem of the non-uniformity of threshold voltages. Another factor affecting the uniformity of brightness is internal resistance. Since the lines have internal resistance and OLEDs are light emitting devices driven by currents, as long as there are currents passing through the lines, there must be voltage drops in the lines, directly resulting that power supply voltages at different positions cannot reach the required voltage.
Second, OLED involves the aging problem which is a common problem that all displays based on OLED emitting must face. Since DC (direct current) driving is mostly used in the prior art, the transport directions of holes and electrons do not change, and the holes and electrons are injected into the light emitting layer from the anode and the cathode respectively to form excitons in the light emitting layer to emit light through irradiation. The remaining holes (or electrons) which are not involved in recombination may accumulate at the hole transport layer/light emitting layer interface (or the light emitting layer/electron transport layer interface) or flow into the electrodes over the potential barrier. With the increasing of the usage time of the OLED, lots of un-recombined carriers (including holes and electrons) accumulated at the internal interfaces of the light emitting layer build a built-in electric field inside the OLED, causing the threshold voltage Vth_oled of the OLED to increase constantly, the illumination brightness of the OLED to drop constantly, and the energy utilization efficiency to decrease gradually.